OM's,
I can assure you that running a dipole through a tree can cause RF to arc to
the branches and burn/ignite a branch on the tree. It depends upon how you
are feeding the antenna (coax vs open wire feeders) and where the current
and voltage nodes appear throughout the length of the antenna. With QRO and
shortened antennas fed with ladder line and high power, you can create
significant current and voltage nodes where the element wire runs adjacent
to tree branches. This occurs even with insulated wire. This morning, I am
about to add some ADDITIONAL insulation to my modified Alpha Delta 100 foot
long 40/80/160 mtr inverted V which I feed with Ladder line, using vinyl
tubing bought in your local plumbing department. Hopefully, that will
provide enough insulation for the portion of the element wire that runs
through the tree in my front yard, lest I too have a "burning bush" at my
house.
By the way, whatever little attenuation the tree imparts to my signal, has
not limited me from working the world on 75/80 mtrs this winter, so enough
signal is definitely getting out from St. Louis to Europe, Africa and the
Pacific.
73,
Dave, K2DP
----- Original Message -----
From: "Rob Atkinson, K5UJ" <k5uj@hotmail.com>
To: <tentec@contesting.com>
Sent: Saturday, February 04, 2006 7:51 AM
Subject: [TenTec] re Trees
The topic of trees has come up elsewhere (towertalk and a broadcast
reflector i read) and i can say from reading them that the consensus is
that
trees attenuate RF if they are in the near field. this is why mw and sw
broadcasters clear trees off their sites but, it isn't always such a big
problem that you should abandon the idea of putting your vertical dipole
amongst them. I would be more concerned about pine tree contact with the
high v. end of ur dipole and burning. Have not experienced this myself
(and being a chicken i hired a guy to trim a pine tree away from part of
my
loop) and nothing may happen in your case, but if i were you and i ran
QRO,
i'd rest easier if I could position the wire so that it's a few feet from
any branches and needles, or if that isn't possible, trim anything making
contact back a few feet. Some guys say they get around this by using
insulated wire, but I have also read that the insulation can rub off
eventually.
rob / k5uj
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